The method of producing a fluoropolymer aqueous dispersion generally comprises carrying out the polymerization in an aqueous medium in the presence of a fluorine-containing emulsifier. It has so far been demanded that concentration of the fluorine-containing emulsifier contained in the aqueous dispersion obtained after polymerization be as low as possible so as not to influence the physical properties, among others, of the moldings obtained therefrom, without deteriorating the dispersion stability of fluoropolymer particles.
As a method of producing fluoropolymer aqueous dispersions reduced in fluorine-containing emulsifier concentration, there is disclosed the method comprising adding a nonionic surfactant to the aqueous dispersion after polymerization and then contacting the mixture with an anion exchange resin to thereby remove the fluorine-containing emulsifier (cf. e.g. Patent Document 1: Japanese Kohyo Publication 2002-532583).
This production method, however, has a problem; the nonionic surfactant added to the fluoropolymer aqueous dispersion obtained mostly remains in the dispersion.
As another method of producing fluoropolymer aqueous dispersions reduced in fluorine-containing emulsifier concentration, there is disclosed the method of a polytetrafluoroethylene aqueous dispersion comprising adding water and a specific nonionic surfactant to the aqueous dispersion obtained after carrying out the polymerization in the presence of a perfluorocarboxylic acid type surfactant and then subjecting the mixture to electric concentration (cf. e.g. Patent Document 2: Japanese Kokai Publication 2003-268034).
This production method, however, has a problem; the nonionic surfactant added to the fluoropolymer aqueous dispersion obtained mostly remains in the dispersion, because the production method comprises the step of adding the specific nonionic surfactant before the electric concentration.